[DOC] migrate _output and _decomposition docstrings to numpydoc style#2120

Meet-Ramjiyani-10 wants to merge 2 commits intosktime:mainsktime/pytorch-forecasting:mainfrom

Meet-Ramjiyani-10:doc/migrate-output-decomp-numpydocMeet-Ramjiyani-10/pytorch-forecasting:doc/migrate-output-decomp-numpydocCopy head branch name to clipboard